(1) Field of the Invention
The present invention relates to an olefin thermoplastic polymer composition. More specifically, the present invention relates to an olefin thermoplastic polymer composition superior in mechanical strength, appearance and moldability.
(2) Description of the Related Art
As well known in the art, a thermoplastic elastomer composition has been obtained by so-called dynamic cross-linking, according to which a rubber like polymer such as a radical cross-linking olefin elastomer and a non-radical cross-linking olefin resin such as polypropylene are melt-kneaded and cross-linked in an extruder in the presence of a radical initiator. The elastomer composition has been extensively applied for various uses such as car parts.
As such an olefin elastomer, ethylene-propylene-diene rubber (EPDM) and an elastomer produced using a metallocene catalyst (JP-A 8-120127 and JP-A 9-137001) are known. However, those mentioned above are not always sufficient in their appearance and moldability, and particularly when a cross-linking degree is increased for the purpose of improving mechanical strength and oil resistance, a huge dispersion product owing to cross-linked rubber is produced to markedly deteriorate the mechanical strength and appearance.
On the other hand, as a prior art for improving physical properties of the olefin rubber obtained by the dynamic cross-linking, there are disclosed a process for producing a thermoplastic rubber composition by cross-linking an olefin rubber and an olefin resin, characterized in that a dynamic heat treatment is repeated more than one time (JP-A-58-145741), a process for producing a rubber composition by adding an organic peroxide, namely a cross-linking agent on the way (JP-A-9-95540), a process for producing a rubber composition by adding a master batch of an organic peroxide and a polypropylene resin on the way (JP-A-6-170914), and a production process comprising kneading the whole of a rubber component and a part of a cross-linking agent to perform cross-linking, thereafter kneading a resin component therewith and further kneading the remaining cross-linking agent therewith to complete cross-linking (JP-A-2002-194096). However, balance characteristics of the mechanical strength, oil resistance and appearance are not sufficient, and therefore, a thermoplastic elastomer composition sufficient to practical use has been desired.
Under these circumstances, an object of the present invention is to provide an olefin thermoplastic polymer composition, which is freed from the problems mentioned above, in other words, which is superior in its mechanical strength, appearance and moldability.
The present inventors have undertaken extensive studies to find an olefin thermoplastic polymer composition superior in its mechanical strength, appearance and moldability. As a result, it has been found that when a rubber like polymer has a specific particle diameter, surprisingly, not only its appearance but also its mechanical strength and its moldablity can be far improved. Thereby, the present invention has been obtained.
That is, the present invention provides an olefin polymer composition, which comprises a cross-linked olefin polymer composition comprising at least one cross-linking rubber like polymer (A) and an olefin resin (B), the cross-linking rubber like polymer (A) being selected from the group consisting of (1) an ethylene-xcex1-olefin copolymer, which contains an ethylene unit and an xcex1-olefin unit having 3 to 20 carbon atoms, and which is produced by using a metallocene catalyst, and (2) at least one hydrogenated rubber selected from the group consisting of a homopolymer of a conjugated diene monomer and a copolymer thereof, in which rubber not less than 50% of all olefinic double bonds are hydrogenated, wherein the cross-linking rubber like polymer (A) has a weight average particle diameter of from 0.01 to 3 xcexcm.
Further, the present invention provides a process for producing an olefin polymer composition, which comprises cross-linking the above-defined (A) and (B) with a cross-linking agent (C) at a melt viscosity ratio xcex7A/xcex7B of from 0.5 to 5, where xcex7A and xcex7B are measured under conditions of a melting temperature of 200xc2x0 C. and a shearing speed of 1000 l/sec at a temperature of from a temperature lower by 30xc2x0 C. than a one minute decomposition half-life temperature T1/2 of the cross-linking agent (C) to a temperature higher by 30xc2x0 C. than the T1/2 to the extent of a cross-linking degree of not less than 30%, in which process particularly preferably the cross-linking agent (C) is separately added more than one time.
The thermoplastic polymer composition in accordance with the present invention is superior in mechanical strength, appearance and moldability.
The composition in accordance with the present invention can be extensively applied for various uses such as car parts, car interior materials, air-bag covers, machine parts, electrical parts, cables, hoses, belts, toys, miscellaneous goods, daily necessaries, building materials, sheets and films, and can play a major role in industry.